Silicoaluminophosphates having an AEL structure, and their preparation

ABSTRACT

Disclosed are silicoaluminophosphates (SAPOs) having unique silicon distributions and their preparation. More particularly, the new SAPOs have a high silica:alumina ratio, and are prepared from single phase synthesis solutions, or from microemulsions containing surfactants.

This application claims benefit of Provisional application No.60/086,681, filed May 26, 1998.

FIELD OF THE INVENTION

This invention relates to silicoaluminates (SAPOs) having unique silicondistributions, a method for their preparation and their use ascatalysts. More particularly, the new SAPOs, designated ECR-42 herein,have a high silica:alumina ratio and a beneficial silicon atomdistribution.

BACKGROUND OF THE INVENTION

The preparation of crystalline silicoaluminophosphates is well known.U.S. Pat. No. 4,480,871 describes the preparation of crystalline,microporous silicoaluminophosphates by hydrothermal crystallization ofsilicoaluminophosphate gels containing a molecular structure formingtemplate. SAPOs are members of a class known as non-zeolitic molecularsieves. The SAPO molecular sieve has a framework of AlO₄, SiO₄ and PO₄tetrahedra linked by oxygen atoms. The negative change in the network isbalanced by the inclusion of exchangeable protons or cations such asalkali or alkaline earth metal ions. The interstitial spaces of channelsformed by the crystalline network enables SAPOs to be used as molecularsieves in a manner similar to crystalline aluminosilicates such aszeolites.

Accordingly, numerous microporous framework structures analogous to thealuminosilicate zeolites can be synthesized having an AlPO₄ compositionand have been called ALPOs. A modified family of materials has been madeby the substitution of Si⁴⁺ for Al³⁺ and P⁵⁺ (SAPOs). Although the ALPOstructures are neutral frameworks, the substitution of Si⁴⁺ for P⁵⁺imparts a negative charge on the framework. By suitable choice of acation, this can be translated into catalytic activity. However,alternate substitutions may be possible that may result in adisproportionately low exchange capacity. The exact nature of Sisubstitution into ALPO structures is complex and highly variable and maydepend on both the topology of the ALPO/SAPO and the method ofpreparation. The result is that preferred catalysts may be made by asuitable choice of synthesis method. For example, SAPO-5 and SAPO-11 maybe conventionally prepared in an aqueous solution or frommicroemulsions. The latter processes use hexanol and a cationic orneutral surfactant to a two-phase gel leading to the formation of amicroemulsion.

The microemulsion process is a two-phase approach to preparing SAPOsattempts to reduce the amount of undesirable silica island formation bysupplying the silicon from an organic phase to the aqueous phase at alow concentration during crystallization. The organic phase contains theorganic solvent and organic silicon source, tetraethylorthosilicate,which is only slightly soluble in the aqueous phase. The aqueous phaseis where crystallization occurs and contains the phosphorous andaluminum. It has been theorized that as the silicon is depleted from theaqueous phases by the growing SAPO crystals, it will be replenished fromthe organic phase, thereby forming a silicoaluminophosphate producthaving a more uniform distribution of silicon in the framework.

SAPOs have application for a wide variety of uses, for example ascatalysts. In this regard, it is known that increasing Si concentrationat first results in an increase in catalystic activity. However,increasing Si content beyond about 0.04 mole fraction in the framework,based on the total amount of silicon, aluminum, and phosphorous in theframework, provides no increase in activity, and may even lead to adecrease, depending on the specific distribution and clustering of theSi⁴⁺ substituent.

In that the distribution of Si in the SAPO framework affects catalyticactivity, the catalytic activity of SAPOs therefore depends on both theglobal composition and the Si distribution. Accordingly, SAPOs aredefined not only by chemical composition and X-Ray Diffraction, but alsoby ²⁹Si MAS NMR spectra which define the Si distributions. On the basisof this last technique, it has been shown that when the SAPOs containlow amounts of Si, the silicon atoms are mostly isolated. However, whenthe Si content increases, Si islands start to appear, i.e., Si siteshaving silicon atoms and no aluminum atoms in neighboring latticepositions.

It would, therefore, be desirable to further increase silicon content inSAPO molecular sieves without forming undesirable silica islands inorder to increase catalytic activity and selectivity.

SUMMARY OF THE INVENTION

In one embodiment, the invention is a composition comprising a molecularsieve with a framework tetrahedra of silicon, aluminum, and phosphorus,and designated ECR-42, the composition having a total silicon amountranging from above about 4 molar percent to about 20 molar percent, atotal aluminum amount ranging from about 40 molar percent to about 55molar percent, and a total phosphorus amount ranging from about 30 molarpercent to about 50 molar percent, the molar percents being based on thetotal amount of aluminum, phosphorus, and silicon present in thecomposition, and the molecular sieve having the topology AEL and beingisostructural with conventional SAPO-11, wherein

(a) the silicon present in the molecular sieve and the conventionalSAPO-11 is distributed among silicon sites in the framework tetrahedra,each site having a first, a second, a third, and a fourth nearestneighbor position, and each next nearest neighbor position beingindependently occupied by one atom selected from silicon, and aluminum,and

(b) the molecular sieve has a substantially smaller number of siliconsites having silicon atoms among all four nearest neighbor positionsthan the conventional SAPO-11 with the total silicon amount.

In another embodiment, the invention is a composition comprising amolecular sieve with a framework tetrahedra of silicon, aluminum, andphosphorus, the composition having a total silicon amount ranging fromabove about 4 molar percent to about 20 molar percent, a total aluminumamount ranging from about 40 molar percent to about 55 molar percent,and a total phosphorus amount ranging from about 30 molar percent toabout 50 molar percent, the molar percents being based on the totalamount of aluminum, phosphorus, and silicon present in the composition,and the molecular sieve having the topology AEL and being isostructuralwith conventional SAPO-11, wherein

(a) the molecular sieve has a first number of Si atoms coordinated as Si(4 Si),

(b) the conventional SAPO-11 has a second number of Si atoms coordinatedas Si(4 Si), and

(c) the first number of Si atoms is substantially less than the secondnumber of Si atoms.

In another embodiment, the invention is a method for forming a molecularsieve composition, the method comprising:

(a) combining at least one water-dispersible phosphorus source material,at least one template capable of structure directing to AEL, water, anda water-soluble or dispersible organic silicon source material undergellation conditions in order to form a gel, and then

(b) reacting the gel under molecular sieve synthesis conditions.

In another embodiment, the invention is a product formed in accordancewith such a process

In another embodiment, the invention is a silicoaluminophosphate gelformed by combining under gellation conditions at least onewater-dispersible silicon source material, at least one template capableof structure-directing to AEL, at least one water-dispersible phosphorussource material, and water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the type of silicon environments in SAPO-typemolecular sieves.

FIG. 2 shows a representative deconvolution of an ²⁹Si NMR spectrum.

FIG. 3 shows the ²⁹Si NMR spectra of conventionally prepared SAPO-11.Spectrum 3(a) shows a SAPO-11 of 5 molar percent Si having about ⅓ ofthe Si atoms located in silicon islands. Spectrum 3(b) is a SAPO-11 of 4molar % Si having at most a small amount of Si located in Si islands,and spectrum 3(c) shows a SAPO-11 of 14 molar % Si having extensive Siisland formation.

FIG. 4 shows powder x-ray diffraction data for the AEL-type SAPOsprepared in examples 1 through 4.

FIG. 5-shows powder x-ray diffraction data from AEL-type SAPOs ofexamples 5 through 8.

FIG. 6(a) shows scanning electron micrographs of an AEL-type SAPOprepared in accordance with the method of Example (4), and

FIG. 6(b) shows an electron micrograph of conventionally-preparedSAPO-11.

FIG. 7 shows the ²⁹Si NMR spectra of ECR-42 having framework silicon inamounts ranging from about 5 molar % to about 13 molar %. Spectrum 7(a)shows ECR-42 with about 13 molar percent Si and having about 9% of theSi atoms located in silicon islands, representing a substantiallyreduced amount of framework Si in islands compared to conventionalSAPO-11 of about the same Si content (FIG. 3(c). Spectrum 7(b) is ofECR-42 of example 6 containing about 7 molar % Si and having about 10%of the Si located in Si islands, and spectrum 7(c) shows an ECR-42 ofexample 1 containing about 4 molar % Si having about 4% of the Silocated in Si islands.

DETAILED DESCRIPTION OF THE INVENTION

The invention is based in part on the discovery that SAPO materialshaving the AEL topology and designated ECR-42 herein may be preparedwith high silicon concentration and without undesirable silicon islandformation. The invention is also based on the discovery that a SAPOprecursor gel such as a silicoaluminophosphate gel may be formed from anaqueous synthesis solution containing no added alcohol or surfactantprovided the co-solvent is a soluble species capable of maintaining ahigh dispersion of silica in a synthesis solution. While not wishing tobe bound by any theory or model, the co-solvent is believed to inhibitpolymerization of the highly dispersed silica species. The preferredmethods therefore provide a SAPO molecular sieve containing Si in thetetrahedral framework at a concentration above about 0.04 molar fraction(based on the total amount of aluminum, silicon, and phosphorous in theframework) and having a desirable Si distribution in the framework,resulting in high catalytic activity and selectivity.

In other words, it has been discovered that modifying the synthesis of asilicon-substituted aluminophosphate by changing the composition of thesynthesis mixture, the synthesis conditions, or both, modifies thesilicon distribution in the silicoaluminophosphate thus formed. Thischanged distribution of silicon may have a major beneficial influence onthe catalytic activity of the silicoaluminophosphate.

Accordingly, when AEL-type molecular sieve materials are synthesizedfollowing the procedure described herein, the distribution of Si andtherefore the total number and strength of acid sites in the molecularsieve framework is quite different, and much higher than those ofpreviously reported forms of SAPO molecular sieves.

The preferred silicoaluminophosphate composition of this invention,ECR-42, has the topology AEL which corresponds to SAPO-11. The AELtopology is defined in the “Atlas of Zeolite Structure Types,” 4th Ed,by W. M. Meier, D. H. Olson and Ch. Baerlocher, Elsevier, 1996. Althoughthe composition is isostructural with other AEL molecular sievematerials, it is a distinct molecular sieve composition because thesilicon, aluminum, and phosphorus atoms are not arranged the same way asin conventional SAPO-11 molecular sieve. Those skilled in the art willrecognize that two isostructural molecular sieves may be entirelydifferent compositions having entirely different properties, dependingon, for example, the nature and distribution of the constituent atoms.

Preferred molecular sieve compositions are physically different fromother SAPO's having the AEL structure because the silicon atoms aredistributed differently in the molecular sieve framework. The physicalstructure of the preferred composition (and its silicon distribution) isillustrated schematically in FIG. 1. While the actual structure is threedimensional and contains oxygen in addition to silicon, aluminum andphosphorus, the figure's atomic positions are represented on a twodimensional array and oxygen atoms are omitted for clarity. As is shownin the figure, each lattice site in the framework has four nearestneighbor lattice sites. In the preferred compositions, as with allAEL-type SAPOs, a lattice site occupied by a silicon 4+ cation, i.e., a“silicon site”, ordinarily may not have a phosphorous 5+ cation as anearest neighbor. The four nearest neighbor lattice sites may thereforebe occupied by one silicon and three aluminum cations, two silicon andtwo aluminum cations, three silicon and one aluminum cations, foursilicon cations, or four aluminum cations. As discussed, conventionalAEL-type SAPOs with increased silicon concentration, above about 4 molar%, contain undesirable silicon islands, i.e., silicon atoms in theframework having four silicon atom nearest neighbors. The silicon atomsin the preferred composition are physically distributed so that thesilicon island concentration is greatly reduced compared withconventional SAPO-11 (i.e., SAPO-11 prepared in accordance with themethods disclosed in the prior art) having the same total siliconconcentration.

In a particularly preferred embodiment, the total molar fraction ofsilicon in the ECR-42 framework is greater than about 0.05, and thenumber of Si atoms having no Si nearest neighbor ranges from about 0mol. % to about 100 mol. %, the number of Si atoms having one Si nearestneighbor ranges from about 5 mol. % to about 25 mol. %, the number of Siatoms having two Si nearest neighbors ranges from about 0 mol. % toabout 35 mol. %, the number of Si atoms having three Si nearestneighbors ranges from about 0 mol. % to about 25 mol. %, and the numberof Si atoms having four Si nearest neighbors ranging from about 0 mol. %to about 25 mol. %, the mol. % being based on the total silica in theECR-42.

Preferably, the ECR-42 compositions have a Si content ranging from aboveabout 4 mol. % to about 20 mol. %, more preferably from about 5 mol. %to about 15 mol. %, and still more preferably from about 7 mol. % toabout 15 mol. %, the silicon content being based on the total amount ofSi present in the framework of the molecular sieve composition.Preferably, more than about 50 molar %, and more preferably more thanabout 90 molar % of the silicon atoms present in the framework do nothave four silicon atoms as nearest neighbors in the framework.

The preferred molecular sieve compositions have both a desirably highsilicon concentration and a desirable silicon atom dispersion (i.e., asmaller number of silicon islands than would be present in conventionalSAPO-11 with the same silicon content) may be formed in accordance withconventional molecular sieve synthesis techniques. The preferred ECR-42synthesis processes commence with the formation of asilicoaluminophosphate gel having the formula

X₁SURF:X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₂:X₄H₂O:X₅SOL

wherein SURF is a surfactant capable of forming a microemulsion betweensynthesis solution's organic and aqueous phases. While not wishing to bebound by any theory or model, it is believed that the surfactant helpsto solubilize the organic tetraalkylorthosilicate silica source and alsoincreases the available interface between the organic species andinorganic species in the synthesis gel resulting in an improvement inthe final silica distribution in the silicoaluminophosphate product.Non-limiting examples of useful surfactants include one or more of longchain alkylamines such as hexadecylamine, tetradecylamine, dodecylamine,decylamine, or octylamine, or dimethyl alkylamine compounds such asdimethylhexadecylammine or dimethyloctylamine, or trimethylalkylammoniumsalts such as trimethylhexadecylammounium chloride.

TEMP is a template capable of structure directing to AEL such asdi-n-propylamine, diisopropylamine, or diethylamine for forming thepreferred ECR-42 silicoaluminophosphate molecular sieve.

SOL is a water-soluble organic co-solvent capable of solubilizing theorganic silicon source. While not wishing to be bound, it is believedthat solubilizing organic silicon sources such as atetraalkylorthosilicate silicon source into the aqueous synthesis gelimproves the final silicon distribution in the silicoaluminophosphateproduct. Non-limiting examples of useful water-soluble organic solventsinclude one or more of acetone, 1,2-propanediol, 1,3-propanediol,methanol, ethanol, propanol, isopropanol, butanol, or ethylene glycol.

The silicon source material may be any silicon species capable of beingdispersed or dissolved in an aqueous synthesis solution. As discussed,where an organic silicon species is employed, a water-soluble organicsolvent, SOL, is preferably employed. While not wishing to be bound byany theory or model, it is believed dispersing the silicon species in alow molecular weight form in the silicoaluminophosphate synthesis gelimproves silicon distribution of the preferred ECR-42 material formedtherefrom. Non-limiting examples of useful silicon source materialsinclude one or more of tetraalkylorthosilicates such astetramethylorthosilicate, tetraethylorthosilicate,tetrapropylorthosilicate, tetrabutylorthosilicate, andsilsesquisiloxanes having up to twelve Si centers.

X₁ ranges from about 0 to about 0.5, X₂ ranges from about 0.1 to about4, X₃ ranges from about 0.01 to about 2, X₄ ranges from about 10 toabout 100, and X₅ ranges from about 0 to about 30. Thesilicoaluminophosphate gel may be formed in accordance with thefollowing processes.

(I) Processes using surfactant and water-soluble co-solvent

Silicoaluminophosphate gels having the formula

X₁SURF:X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₂:X₄H₂O:X₅SOL

may be prepared by combining a phosphorus source such as H₃PO₄, ammoniumphosphate, and mixtures thereof; water; and an aluminum source such ashydrated alumina, organo alumina, pseudo-boehmite, aluminum hydroxide,colloidal alumina, and mixtures thereof, and then adding the template inorder to form a homogeneous alumino phosphate mixture. The P₂O₅:Al₂O₃molar ratio in the alumino phosphate mixture preferably ranges fromabout 0.7 to about 1.3, and more preferably ranges from about 0.9 toabout 1.1. The TEMP:Al₂O₃ molar ratio in the alumino phosphate mixturepreferably ranges from about 0.1 to about 5, and more preferably fromabout 0.5 to about 3. A surfactant solution of the surfactant, thewater-soluble organic solvent, and water may then be added to thealumino phosphate mixture along with the organic silicon source andwater (if necessary to obtain the desired value of X₄) in order to forma synthesis solution having a SURF:Al₂O₃ molar ratio preferably rangingfrom about 0 to about 0.5, and more preferably ranging from about 0.05to about 0.3. The relative amounts of the ingredients for the synthesissolution may be calculated from the desired values of X₁ through X₅. TheSOL:Al₂O₃ molar ratio in the synthesis solution preferably ranging fromabout 0 to about 30, and more preferably ranging from about 4 to about20, and the SiO₂:Al₂O₃ molar ratio preferably ranging from about 0.01 toabout 2.0, and more preferably ranging from about 0.1 to about 0.8. Thesynthesis solution may then be subjected to gel formation conditions inorder to provide the silicoaluminophosphate gel. The ingredients of thesynthesis solution, surfactant solution, and alumino phosphate mixturemay be mixed in any order. For example, in an alternative embodiment theorganic silicon source may be added to a mixture of phosphoric acid andthe water-soluble organic solvent. The template and the surfactant maythen be added, with the water and aluminum source being added last.

Preferred silicoaluminophosphate crystallization conditions for formingthe ECR-42 molecular sieve from the gel include heating the gel in amicrowave autoclave for a time sufficient to crystallize the gel. Lowertemperature and shorter crystallization times are preferred because suchconditions may prevent the formation of undesirable products.Accordingly, the preferred heating times range from about 1 minute toabout 5 days, at a temperature ranging from about 100° C. to about 250°C., and at a pressure ranging from about 0 bar to about 70 bar. In caseswhere other products, unreacted gel, or a mixture thereof is present atthe conclusion of the reaction, the molecular sieve may be recovered bya separation process such as centrifugation. The process may alsoinclude conventional product washing and drying such as an ethanolrinse, followed by a water rinse, followed by air oven drying at atemperature ranging from about ambient temperature to about 200° C. Itshould be noted that conventional heating, in for example an air oven oran externally heated autoclave, may be substituted for microwave heatingin this process, and that a substantially pure ECR-42 molecular sievecomposition having the AEL-topology will result with either heatingmethod. When conventional heating is used, the temperature preferablyranges from about 100° C. to about 250° C., and more preferably from150° C. to about 200° C.

(II) Processes using surfactant, hexanol co-solvent and microwaveheating

Silicoaluminophosphate gels having the formula

X₁SURF:X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₄:X₂H₂O:X5SOL′

wherein SOL′ is a relatively water insoluble organic solvent includingsolvent mixtures capable forming a microemulsion with water and asurfactant, and including mixtures thereof, may be prepared by accordingto the method (I) above, except that the water insoluble organic solventSOL′ is substituted for the water-soluble solvent SOL. But for thesolvent substitution, the molar ratios of the ingredients in the aluminophosphate mixture and the synthesis solution are as set forth in method(I), and as in that method, the mixing order is not critical.

The preferred ECR-42 molecular sieve composition may be formed from thegel in accordance with the steps set forth in process (I). It should benoted that conventional heating may result in the presence of SAPO-41material in the molecular sieve composition.

(III) Processes using ethanol with water-soluble co-solvent and no addedsurfactant

Silicoaluminophosphate gels of stoichiometry:

X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₂:X₄H₂O:X₅SOL

may be prepared by a method identical to method (I), above, except thatno surfactant solution is used. An aqueous solution of water, thewater-soluble organic solvent, and the silicon source is used instead ofthe surfactant solution. But for the absence of the surfactant, themolar ratios of the ingredients in the alumino phosphate mixture and thesynthesis solution are as set forth in method (I), and as in thatmethod, the mixing order of the ingredients is not critical.

The preferred ECR-42 molecular sieve composition may be formed from thegel in accordance with the steps set forth in process (I).

(IV) Processes using an organic silicon source and no added surfactantor water-soluble organic cosolvent

Silicoaluminophosphate gels of stoichiometry:

X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₂:X₄H₂O

may be prepared by a method identical to method (I), above, except thatno surfactant and no co-solvent are employed. An aqueous dispersion ofwater, and an organic silicon source such as TEOS, including mixturesthereof, is used instead of the surfactant solution.

But for the absence of the surfactant, the molar ratios of theingredients in the alumino phosphate mixture and the synthesis solutionare as set forth in method (I), and as in that method, the mixing orderof the ingredients is not critical.

The preferred ECR-42 molecular sieve composition may be formed from thegel in accordance with the steps set forth in process (I). The productmay contain SAPO-31.

(V) Processes for forming SAPO-11 using colloidal silica with no addedsurfactant and no added solvent

Silicoaluminophosphate gels of stoichiometry:

X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₂:X₄H₂O

may be prepared by a method identical to method (I), above, except thatno surfactant solution is used. An aqueous dispersion of water and thecolloidal or fumed silica is used instead of the organic silicon sourceand surfactant solution. But for the absence of the surfactant andco-solvent, the molar ratios of the ingredients in the alumino phosphatemixture and the synthesis solution are as set forth in method (I), andas in that method, the mixing order of the ingredients is not critical.

A SAPO-11 molecular sieve composition may be formed from the gel inaccordance with the steps set forth in process (I). The product maycontain SAPO-31.

The preferred ECR-42 molecular sieve compositions are crystalline, andmay be prepared with crystal sizes ranging from about 0.001 micrometersto about 1.0 micrometers. Preferably, crystal size ranges from about0.01 micrometers to about 0.5 micrometers. The synthesis may be adjustedto prepare crystals of decreased size by diluting the synthesis solutionwith surfactant, co-solvent, and mixtures thereof. Small crystals mayalso be prepared by conventional methods such as seeding and high shearagitation rates.

Molecular sieve materials prepared in accordance with these methods areuseful as catalytic materials. A non-limiting description of thecatalytic nature and some catalytic uses of such materials is asfollows.

As is known to those skilled in the art, molecular sieve materials maypossess an intrinsic or added catalytic functionality, and suchmaterials are frequently referred to as “molecular sieve catalysts”.Additional catalytic functionalities may be provided for molecular sievematerials by conventional methods. Such methods are applicable to thepreferred molecular sieves, and may be summarized as follows.

Accordingly, the molecular sieve material formed from the gel as setforth above may be calcined to remove the template. The sample may thenbe allowed to cool, preferably in the presence of a dessicator, and thenloaded with a catalytically active species such as Pt by conventionaltechniques such as incipient wetness.

The preferred catalytic molecular sieve compositions are useful for atleast hydrocarbon isomerization, hydrotreating, and cracking such ashydrocracking and fluid catalytic cracking, especially naphtha cracking.The preferred ECR-42 molecular sieve compositions have a dramaticallyincreased catalytic activity for such processes over AEL type SAPOmolecular sieves prepared by conventional techniques.

More specifically, the preferred ECR-42 molecular sieves may be used inapplications including, but not limited to, catalytic dewaxing,isodewaxing/isomerization, hydrocracking, alkylation of aromatichydrocarbons (e.g., benzene) with long chain olefins (e.g., C₁₄ olefin),alkylation of aromatic hydrocarbons (e.g., benzene and alkylbenzenes) inpresence of an alkylating agent (e.g., olefins, formaldehyde, alkylhalides and alcohols having 1 to about 20 carbon atoms), alkylation ofaromatic hydrocarbons (e.g., benzene) with light olefins to produceshort chain aromatic compounds (e.g., alkylation of benzene withpropylene to give cumene), transalkylation of aromatic hydrocarbons inthe presence of polyalkylaromatic hydrocarbons, isomerization ofaromatic feedstock components (e.g., xylene), naphtha cracking to makeolefins, oligomerization of straight and branched chain olefins havingfrom about 2 to 5 carbons atoms, diproportionation of aromatics (e.g.,the disproportionation of toluene to make benzene and paraxylene), andconversion of naphtha (e.g., C6-C10) and similar mixtures to highlyaromatic mixtures.

In summary, it has been discovered that when AEL-type molecular sievesare preferably synthesized in accord with the methods described herein,that the distribution of Si and therefore the total number and strengthof acid sites is quite different, and much higher, than those ofconventional SAPO-11. It has also been discovered that the preferredmolecular sieves are extremely active and selective for carrying outreactions of hydrocarbon such as alkylation, disproportionation,oligomerization, naphtha cracking and other reactions known to involvemolecular sieve catalysts, especially the catalytic dewaxing andisodewaxing of hydrocarbon feeds containing paraffins.

The invention is further exemplified by the following non-limitingexamples.

EXAMPLES

I. Preparation of the Preferred ECR-42 Molecular Sieves

Example 1

Preparation of ECR-42 using surfactant, ethanol co-solvent, andmicrowave heating

A silicoaluminophosphate gel of stoichiometry:

0.16 CA: DPA: Al₂O₃: P₂O₅: 0.2 SiO₂: 50.3 H₂O: 7.3 ethanol

(where CA is hexadecylamine) was prepared by mechanically mixingtogether 28.6 grams of H₃PO₄(85%), 25 grams of water and 17 grams ofCatapal B alumina (Vista Chemical Co., Houston, Tex. 74% Al₂O₃, 26% H₂Ofor 45 min. in a 500 ml Teflon bottle until homogeneous. To this mixturewas added 12.7 grams of DPA, and the mixture was then stirred for 30minutes. A surfactant solution was prepared by mixing 2.4 grams ofhexadecylamine in 20.8 grams of ethanol and 12.5 grams of water. Thissolution was added to half of the di-n-propylamine/aluminophosphatemixture along with 2.6 grams of TEOS and 11.2 grams of water. Theresulting mixture was stirred for about 3 min. in a 125 ml blender. Thisgel was divided between three CEM XP-1500 Teflon microwave autoclaves(about 28.5 grams each), available from CEM Corp., Matthews, N.C. Thethree autoclaves were heated for 5 min. in a microwave oven to apressure of 485 psi. After 5, 30 and 60 min. at 485 psi the samples wereremoved from the oven. The ECR-42 products were recovered bycentrifugation and washed twice with ethanol and then twice withde-ionized water. The resulting products were dried in an air oven at115° C. and the powder X-ray diffraction pattern measured which showedthe products to be pure SAPO-11, see FIG. 4(a). Elemental analysis ofthe 60 min. sample gave: 17.3% Al; 17.0% P; 1.68% Si, representing aproduct stoichiometry of Si_(0.05)Al_(0.51)P_(0.44).

Example 2

Preparation of ECR-42 using surfactant, hexanol co-solvent, andmicrowave heating

A silicoaluminophosphate gel of stoichiometry:

0.16 CA: DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 39 H₂O: 4.5 hexanol

(where CA is hexadecylamine) was prepared by mechanically mixingtogether 28.6 grams of H₃PO₄(85%), 25 grams of water and 17 grams ofCatapal B alumina (Vista, 74% Al₂O₃, 26% H₂O) for 2 hr. in a 500 mlTeflon bottle until homogeneous. To this mixture was added 12.7 grams ofDPA and the mixture was then stirred for 30 minutes. A surfactantsolution was prepared by mixing 4.8 grams of hexadecylamine in 56.9grams of hexanol and 25 grams of water. This solution was added to thedi-n-propylamine/aluminophosphate mixture along with 10.3 grams of TEOSand 22.3 grams of water. The resulting mixture was stirred for about 3min. in a 125 ml blender. This gel was divided between two 125 mlTeflon-lined autoclaves and a CEM XP-1500 Teflon microwave autoclave(about 28.5 grams).

The two autoclaves were heated at 195° C. for 24 and 40 hrs. in aconventional oven. The microwave autoclave was heated for 5 min. in amicrowave oven to a pressure of 485 psi. After 60 min. at 485 psi thesample was removed from the oven. The products were recovered bycentrifugation and washed twice with ethanol and then twice withde-ionized water. The resulting ECR-42 products were dried in an airoven at 115° C. and the powder X-ray diffraction pattern measured showedthat the product of the microwave heating was pure SAPO-11 (FIG. 4(c))and the product of the conventionally heated samples to be SAPO-11 andSAPO-41 (FIG. 4(b)). Elemental analysis of the microwave heated samplegave: 14.5% Al; 16.4% P; 2.84% Si, representing a product stoichiometryof Si_(0.09)Al_(0.46)P_(0.45) and the conventionally heated sample (40hrs.) gave 15.4% Al; 16.4% P; 3.36% Si, representing a productstoichiometry of Si_(0.10)Al_(0.47)P_(0.43).

Example 3

Preparation of ECR-42 using surfactant, ethanol co-solvent, andmicrowave heating

A silicoaluminophosphate gel of stoichiometry:

0.16 CA: DPA: Al₂O₃: P₂O₅: 0.2 SiO₂: 39.1 H₂O: 7.3 ethanol

(where CA is hexadecylamine) was prepared by mechanically mixingtogether 71.5 grams of H₃PO₄(85%), 62.5 grams of water and 42.4 grams ofCatapal B alumina (Vista, 74% Al₂O₃, 26% H₂O) for 45 min. in a 1000 mlTeflon bottle until homogeneous. To this mixture was added 31.7 grams ofDPA and the mixture was then stirred for 30 minutes. A surfactantsolution was prepared by mixing 12 grams of hexadecylamine in 104 gramsof ethanol and 62.5 grams of water. This solution was added to thedi-n-propylamine/aluminophosphate mixture along with 13 grams of TEOSand 56 grams of water. The resulting mixture was stirred for about 3min. in a 250 ml blender. One half of this gel was divided between fiveCEM XP-1500 Teflon microwave autoclaves (about 42.5 grams each). Thefive autoclaves were heated for 10 min. in a microwave oven to apressure of 485 psi. After 30 min. at 485 psi the samples were removedfrom the oven. The ECR-42 products were combined and then recovered bycentrifugation and washed twice with ethanol and then twice withde-ionized water. The resulting product was dried in an air oven at 115°C. and the powder X-ray diffraction pattern measured which showed theproduct to be pure SAPO-11. See FIG. 4(d). Elemental analysis gave:15.96% Al; 17.3% P; 1.638% Si, representing a product stoichiometry ofSi_(0.05)Al_(0.49)P_(0.46).

Example 4

Preparation of ECR-2 using surfactant, ethanol co-solvent and microwaveheating.

A silicoaluminophosphate gel of stoichiometry:

0.16 CA: DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 39.1 H₂O: 7.3 ethanol

(where CA is hexadecylamine) was prepared by adding 6.5 grams more ofTEOS to the second half of the gel prepared in Example 3. Afterthoroughly homogenizing in a blender this gel was divided between fiveCEM XP-1500 Teflon microwave autoclaves (about 42.5 grams each. The fiveautoclaves were heated for 10 min. in a microwave oven to a pressure of485 psi. After 30 min. at 485 psi the samples were removed from theoven. The ECR-42 products were combined and then recovered bycentrifugation and washed twice with ethanol and then twice withde-ionized water. The resulting product was dried in an air oven at 115°C. and the powder X-ray diffraction pattern measured which showed theproduct to be pure SAPO-11. See FIG. 4(e). Elemental analysis gave:15.23% Al; 17.2% P; 2.795% Si, representing a product stoichiometry ofSi_(0.08)Al_(0.46)P_(0.46).

Example 5

Preparation of ECR-2 using surfactant, ethanol co-solvent, andconventional heating

A silicoaluminophosphate gel of stoichiometry:

0.16 CA: 2 DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 40 H₂O: 7.5 ethanol

(where CA is hexadecylamine) was prepared by mixing together 25.4 gramsof H₃PO₄(85%), 35 grams of water, and 15.2 grams of Catapal A alumina(Vista, 74% Al₂O₃, 26% H₂O) for 2 min. in a 250 ml plastic beaker. Tothis mixture was added 22.3 grams of DPA and the mixture was thenstirred for 3 minutes. A surfactant solution was prepared by mixing 4.25grams of hexadecylamine in 38.1 grams of ethanol for thirty minutes.This solution was added to the di-n-propylamine/aluminophosphate mixturealong with 9.18 grams of TEOS and 30.6 grams of water. The resultingmixture was homogenized for about 5 min. in a 250 ml blender. About 80 gof this gel was placed in a 125 Teflon lined autoclave. The autoclavewas heated for 24 hours in an air oven at 195° C. After cooling, theECR-42 product was recovered by centrifugation and washed twice withethanol and then twice with de-ionized water. The resulting product wasdried in an air oven at 115° C. and the powder X-ray diffraction patternmeasured which showed the product to be pure SAPO-11, see FIG. 5(a).Elemental analysis gave: 17.2% Al; 17.1% P; 3.052% Si, representing aproduct stoichiometry of Si_(0.084)Al_(0.491)P_(0.425).

Example 6

Preparation of ECR-42 using TEOS, ethanol co-solvent and conventionalheating

A silicoaluminophosphate gel of stoichiometry:

2 DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 40 H₂O: 7.5 ethanol

was prepared by mixing together 28.9 grams of H₃PO₄(85%), 40 grams ofwater and 17.3 grams of Catapal A alumina (Vista, 74% Al₂O₃, 26% H₂O)for 2 min. in a 250 ml plastic beaker. To this mixture was added 25.4grams of DPA and the mixture stirred for 3 minutes. To thedi-n-propylamine/aluminophosphate mixture was added 43.3 grams ofethanol with 10.4 grams of TEOS and 34.7 grams of water. The resultingmixture was homogenized for about 5 min. in a 250 ml blender. About 80 gof this gel was placed in a 125 Teflon lined autoclave. The autoclavewas heated for 24 hours in an air oven at 195° C. After cooling, theECR-42 product was recovered by centrifugation and washed once withethanol and then three times with de-ionized water. The resultingproduct was dried in an air oven at 115° C. and the powder X-raydiffraction pattern measured which showed the product to be pureSAPO-11. See FIG. 5(b). Elemental analysis gave: 17.94% Al; 20.1% P;2.56% Si, representing a product stoichiometry ofSi_(0.065)Al_(0.473)P_(0.462).

Example 7

Preparation of ECR-42 using TEOS and conventional heating

A silicoaluminophosphate gel of stoichiometry:

1.5 DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 50 H₂O

was prepared by mixing together 25.1 grams of H₃PO₄(85%), 36 grams ofwater and 15 grams of Catapal A alumina (Vista, 74% Al₂O₃, 26% H₂O) for2 min. in a 250 ml plastic beaker. To this mixture was added 16.5 gramsof DPA, and the mixture was stirred for 3 minutes. To thedi-n-propylamine/aluminophosphate mixture was added 9.1 grams of TEOS(tetraethylorthosilicate) and 48.4 grams of water. The resulting mixturewas homogenized for about 5 min. in a 250 ml blender. One half of thisgel was placed in a 125 Teflon-lined autoclave. The autoclave was heatedfor 24 hours in an air oven at 220° C. After cooling, the ECR-42 productwas recovered by centrifugation and washed four times with de-ionizedwater. The resulting product was dried in an air oven at 115° C. and thepowder X-ray diffraction pattern measured which showed the product to beSAPO-11 and SAPO-41. See FIG. 5(c). Elemental analysis gave: 18.8% Al;19.7% P; 2.70% Si, representing a product stoichiometry ofSi_(0.067)Al_(0.49)P_(0.445).

Example 8

Preparation of SAPO-11 using colloidal silica

A silicoaluminophosphate gel of stoichiometry:

1.5 DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 50 H₂O

was prepared by mixing together 31.4 grams of H₃PO₄(85%), 80 grams ofwater and 18.8 grams of Catapal B alumina (Vista, 74% Al₂O₃, 26% H₂O)and mechanically stirring for 0.5 hour in a 500 ml Teflon bottle. Tothis mixture was added 20.7 grams of DPA (di-n-propylamine) and 8.19 gsolution of aqueous colloidal silica (duPont Ludox AS-40, 40% SiO₂) andstirred for 1.5 hours. Finally, 20.9 grams of water were added, and theresulting mixture was homogenized for about 5 min. in a 250 ml blender.This gel was divided between two 125 Teflon lined autoclaves. Theautoclaves were heated for 24 hours in an air oven at 195° C. Aftercooling, the products were combined and then recovered by centrifugationand washed four times with de-ionized water. The resulting product wasdried in an air oven at 115° C. and the powder X-ray diffraction patternmeasured which showed the product to be SAPO-11 and SAPO-31. See FIG.5(d). Elemental analysis gave a product stoichiometry ofSi_(0.056)Al_(0.502)P_(0.442).

Examples 9

Preparation of ECR-42 using various alcohol co-solvents andtetraalkylorthosilicates

A series of silicoaluminophosphate gels of stoichiometry:

X₁CA: 2 DPA: Al₂O₃: P₂O₅: 0.4 SiO₂: 40 H₂O: X₅ SOL

where CA is hexadecylamine and DPA is di-n-propylamine) were prepared bymixing together the appropriate amounts of H₃PO₄(85%), water and CatapalA alumina (Vista, 74% Al₂O₃, 26% H₂O) for 2 min. in a 250 ml plasticbeaker. To this mixture was added the appropriate amount of DPA(di-n-propylamine) and the mixture stirred for 3 minutes. Then theappropriate amount of alcohol, tetraalkylorthosilicate and water wereadded to obtain the stoichiometry as indicated in Table 1. The resultingmixtures were homogenized for about 5 min. in a 250 ml blender. One halfof this mixture was transferred to 125 Teflon-lined autoclave. To theother half was mixed in 1.5 grams of hexadecylamine and also transferredto 125 Teflon-lined autoclave. The autoclaves were heated for 24 hoursin an air oven at 195° C. After cooling the product was recovered bycentrifugation and washed twice with ethanol and then twice withde-ionized water. The resulting products were dried in an air oven at115° C. and the powder X-ray diffraction patterns measured which showedthe products to be pure ECR-42. Elemental analyses and productstoichiometries are listed in Table 2.

TABLE 1 Experiment Si Number X₁ X₅ SOL Source  9 0 11.5 methanoltetraethylorthosilicate 10 .16 11.5 methanol tetraethylorthosilicate 110 6.1 n-propanol tetraethylorthosilicate 12 .16 6.1 n-propanoltetraethylorthosilicate 13 0 6.1 i-propanol tetraethylorthosilicate 14.16 6.1 i-propanol tetraethylorthosilicate 15 0 5.0 n-butanoltetraethylorthosilicate 16 .16 5.0 n-butanol tetraethylorthosilicate 170 8 ethanol tetramethylorthosilicate 18 .16 8 ethanoltetramethylorthosilicate 19 0 8 ethanol tetrapropylorthosilicate 20 .168 ethanol tetrapropylorthosilicate

TABLE 2 Experiment Molar Molar Molar Number % Si % Al % P Si Al P  93.213 18.40 19.37 0.080 0.480 0.440 10 3.870 17.63 13.68 0.112 0.5300.358 11 2.813 20.73 22.22 0.063 0.484 0.452 12 3.542 18.27 15.00 0.0980.526 0.376 13 3.147 18.09 19.42 0.080 0.476 0.445 14 3.550 18.65 15.230.097 0.528 0.376 15 2.668 18.60 19.70 0.067 0.485 0.448 16 3.360 19.3815.78 0.089 0.533 0.378 17 3.148 18.31 19.35 0.079 0.479 0.441 18 4.19418.35 12.98 0.120 0.545 0.336 19 3.124 18.00 19.24 0.079 0.477 0.444 203.730 19.52 15.90 0.097 0.528 0.375

Example 10

The materials of experiments 1-20 were subject to ²⁹Si MAS NMR todetermine the relative amounts of silicon in the five differentenvironments, i.e., Si(4 Si), Si(3 Si), Si(2 Si), Si(1 Si), Si(0 Si).The ²⁹Si Magic-angle spinning (MAS) nuclear magnetic resonance (NMR)spectra with proton decoupling were recorded on a Chemagnetics CMXII 500spectrometer at 99.3 MHz using a 7.5 mm probe spinning at 6 kHz. Typicalrun conditions were: 800 to 10000 acquisitions; 4 or 5 sec. pulse width;60 to 120 sec. relaxation delay. Chemical shifts were measured relativeto tetramethylsilane (TMS). The spectra were then deconvoluted into thefive silicon environments. The molar fractions of each siliconenvironment are given in Table 3.

TABLE 3 Example 4Al, 0Si 3Al, 1Si 2Al, 2Si 1Al, 3Si 0Al, 4Si 1 54 21 139 4 2 3 4 5 49 19 16 11 5 6 33 22 22 13 10 7 8 36 17 7 17 23 9 24 31 1818 9 10 24 44 15 14 3 11 12 13 32 32 22 5 9 14 41 31 6 12 10 15 16 17 3515 10 18 22 18 19 20

Discussion

A. Crystallite Size and Shape

It is well known that zeolite morphology has a major influence on thereactivities of zeolites. Such effects become more important withsmaller pores and larger molecules. At very small crystal sizes, theexterior surface may play a major role in processes using such zeolites,especially the location of exterior pore openings with respect to thecatalytically active site(s).

Powder X-ray diffraction may be used for determining crystallite size(and often shape) of materials less than about 1000 Å by the relativebroadening of peaks in the X-ray diffraction pattern. When the shape ofthe crystallites is anisotrophic (different dimensions in differentdirections), then the resulting powder diffraction pattern may have bothbroad and sharp peaks if one or two of the dimensions of the crystalsare small enough to show peak broadening. Those reflections coming fromMiller planes in the crystals corresponding to the short dimension willhave broader peaks than those coming from Miller planes corresponding tothe longer dimension will have sharper peaks.

SAPO-11 has an orthorhombic crystal structure, a structure which isfrequently associated with spatial anisotropies. The dimensions of theunit cell are a=8.4 Å, b=18.5 Å and c=13.5 Å, and the structure is suchthat the 10-ring channels run along the a dimension [100]. If the shapeof the crystallites was platelet in shape such that the a dimension wassignificantly smaller than the b and c dimensions, one would expect theX-ray diffraction pattern to show the peaks corresponding to the (h00)reflections to be broader than those of the (0k1) reflections. Thiswould result in those peaks corresponding to the (h00) reflections tohave shorter peak height relative to the (0k1) peaks, not due to areduction on peak intensity, but to an increase in the peak width.

While not wishing to be bound by any model or theory, it is believedthat an increased catalytic activity for a molecular sieve catalystwould result when a large number of channel openings are available toallow for efficient transportation of the reacting species and productsto and from the active sites inside of, or at the pore mouth of, themolecular sieve crystal. The preferred ECR-42 molecular sieve catalystshave this desirable spatial anisotropy (preferred orientation), as shownin the powder x-ray diffraction results in FIGS. 4 and 5. The (200)reflections are clearly broader in width and shorter in height thansurrounding (0k1) reflections as the reactants are changed from TEOS(Example 7) to TEOS and ethanol co-solvent (Example 6) to TEOS,surfactant, and ethanol co-solvent (Example 5). The SEM micrograph ofFIG. 6(a) clearly shows the preferred thin platelets present in theproduct of Example 4. The platelets have a thickness less than 50 nm,well within the threshold for seeing X-ray diffraction peak broadening,and consistent with the diffraction patterns in FIGS. 4 and 5. FIG. 6(b)on the other hand, shows the undesirable thick platelet morphology thatresults in conventionally prepared SAPO-11.

B. Silicon Distribution by ²⁹Si NMR

As discussed, while the preferred molecular sieve materials have anX-ray diffraction pattern with line positions corresponding to the AELtopology, they are physically and chemically distinct from known SAPO-11materials because of differences in the local atomic arrangement of thecomponent atoms. Conventional powder x-ray diffraction analysis not asufficient analytical tool to determine the structural differencesbetween SAPO-11 and the preferred ECR-42 molecular sieves partiallybecause of x-ray line broadening, as discussed above. Consequently, inorder to determine the above-noted structural differences, it isnecessary to use an analytical tool which can discriminate between theatomic environment in the overall crystal structure such as ²⁹Si MASNMR, which is well known in the art. An example of how the number or Sinearest neighbors may be derived from NMR data is shown in FIG. 5 andTable 3.

As discussed, it is believed that is the silicon distribution with thecrystal is one important characteristic influencing catalytic activityin SAPO materials. Since silicon is responsible for the acidity in SAPOmaterials, it is desirable that silicon be well dispersed in thealuminophosphate framework for high catalytic activity. It is known thatincreasing silicon concentration in conventionally prepared SAPO-11results in the formation of large silicon islands as shown in FIG. 3(b)(low Si concentration, some island formation) and FIG. 3(c) (high Siconcentration, with extensive island formation). FIG. 3(a) shows thatstill lower Si concentration results in undesirable isolated siliconatoms. Although large silicon islands are undesirable because thosesilicon atoms at the interior of the islands are catalytically inactive,small silicon-rich regions present in the preferred ECR-42 material aredesirable because the strongest acid sites are believed to form at theborders of the Si-rich regions and the aluminophosphate domains. This isbecause those silicons at the borders have fewer aluminum atoms asnearest neighbors, which leads to decreasing acidity resulting fromaluminum's lower electronegativity.

The distribution of silicon in SAPOs may be measured by ²⁹Si NMRspectroscopy. For example, in SAPO-11, it is known that those siliconatoms having 4 aluminums and 0 silicons (4 Al, 0 Si) as nearestneighbors show as NMR resonance at −90 to −93 ppm chemical shiftrelative to tetramethylsilane (TMS). Therefore, the molar percent of Siatoms with zero, one, two, three, and four Si atom nearest neighbors maybe obtained, for example, by deconvoluting the integrated intensitiesfrom ²⁹Si NMR measurements. The Si (4 Al, 0 Si) and the other siliconenvironments are illustrated schematically in FIG. 1 and listed inTable4:

TABLE 4 Si Environment 4Al, 0Si 3Al, 1Si 2Al, 2Si 1Al, 3Si 0Al, 4SiChemical −86 to −95 to −100 to −106 to −109 to shift in ppm −94 ppm −99ppm −105 ppm −108 ppm −115 ppm from TMS

It is clear from the above chart that for well dispersed silicon, a ²⁹SiNMR spectra would have high intensity for the (4 Al, 0 Si) resonance at−86 to −94 ppm, while a poorly dispersed silicon would have highintensity at the (0 Al, 4 Si) resonance at −109 to −115 ppm. Thosesilicons located at the border of the silicon atoms having the highestacid strength would show high relative intensity for the (3 Al, 1 Si),(2 Al, 2 Si), and (1 Al, 3 Si) resonances. FIG. 7 shows ²⁹Si NMR spectraof the preferred ECR-42 molecular sieve with framework Si contents of 4,8, and 13 molar %. The spectra show the excellent silicon dispersion inthe preferred ECR-42 material. By way of comparison, FIG. 3 shows thatSi islanding is avoided in conventional SAPO-11 at very low Siconcentrations only. See FIG. 3(b). At Si content above about 0.04 molefraction, substantial Si islanding occurs. See FIGS. 3(a) and (c). Inparticular, FIG. 7-B, shows that the preferred ECR-42 molecular sievedoes not show undesirable Si island formation at higher Siconcentrations than in the conventionally prepared sample shown in FIG.3(a).

It should be noted that due to the characteristic of the experimentalNMR spectra, the deconvolutions shown in FIG. 2 are not unique, butshould be chosen with chemical sense. Therefore, the simulation resultsconstitute an estimation of the different structural units contributingto the spectra, and may be used to illustrate Si atom coordinationdifferences that are evident from the experimental data.

Moreover, the preferred molecular sieve, ECR-42, may contain Siconcentrations as low as about 1 wt. %, and it is often difficult toobtain high quality NMR data from samples of such a low concentrationover the whole range of chemical shifts. Consequently, some degree ofuncertainty may be introduced into the deconvolutions required todetermine the number of Si atoms with zero, one, two, three and four Sinearest neighbors. Nevertheless, the intensity of the −109 to −115 ppmregion is sufficient in molecular sieve materials of even 1 wt. % todetermine the approximate molar percent of Si framework atoms havingfour Si atom nearest neighbors, i.e., Si atoms located in Si islands.

What is claimed is:
 1. A composition comprising a molecular sieve with aframework tetrahedra of silicon, aluminum, and phosphorus, anddesignated ECR-42, the composition having a total silicon amount rangingfrom above about 4 molar percent to about 20 molar percent, a totalaluminum amount ranging from about 40 molar percent to about 55 molarpercent, and a total phosphorus amount ranging from about 30 molarpercent to about 50 molar percent, the molar percents being based on thetotal amount of aluminum, phosphorus, and silicon present in thecomposition, and the molecular sieve having the topology AEL and beingisostructural with conventional SAPO-11, wherein (a) the silicon presentin the molecular sieve and the conventional SAPO-11 is distributed amongsilicon sites in the framework tetrahedra, each site having a first, asecond, a third, and a fourth next nearest neighbor position, and eachnext nearest neighbor position being independently occupied by one atomselected from silicon and aluminum, and (b) the molecular sieve has asubstantially smaller number of silicon sites having silicon atoms amongall four next nearest neighbor positions than the conventional SAPO-11having the same total silicon amount.
 2. The composition of claim 1wherein the molecular sieve composition's Si content ranges from about 5mol. % to about 15 mol. %.
 3. The composition of claim 2 wherein thenumber of Si atoms in the framework having three Si nearest neighborsranges from about 0 mol. % to about 25 mol. % and the number of Si atomshaving four Si nearest neighbors ranges from about 0 mol. % to about 50mol. %, the mol. % being based on the total amount of silicon in theframework.
 4. The composition of claim 3 wherein the molar % offramework silicon atoms having aluminum atom nearest neighbors ismeasured by ²⁹Si MAS NMR.
 5. A composition comprising a molecular sievewith a framework tetrahedra of silicon, aluminum, and phosphorus, thecomposition having a total silicon amount ranging from about 4 molarpercent to about 20 molar percent, a total aluminum amount ranging fromabout 40 molar percent to about 55 molar percent, and a total phosphorusamount ranging from about 30 molar percent to about 50 molar percent,the molar percents being based on the total amount of aluminum,phosphorus, and silicon present in the composition, and the molecularsieve having the topology AEL and being isostructural with conventionalSAPO-11, wherein (a) the molecular sieve has a first number of Si atomscoordinated as Si(4 Si), (b) the conventional SAPO-11 with the Si amounthas a second number of Si atoms coordinated as Si(4 Si), and (c) thefirst number of Si atoms is substantially less than the second number ofSi atoms.
 6. The composition of claim 5 wherein the number of Si atomshaving four Si nearest neighbors ranging from about 0 mol. % to about 25mol. %.
 7. The composition of claim 6 wherein the molecular sievecomposition's Si content ranges from about 5 mol. % to about 15 mol. %.8. The composition of claim 7 wherein the number of Si atoms having fourSi nearest neighbors ranging from about 0 mol. % to about 10 mol. %. 9.The composition of claim 8 wherein the molar % of framework siliconatoms having aluminum atom nearest neighbors is measured by ²⁹Si MASNMR.
 10. A method for forming a molecular sieve composition, the methodcomprising: (a) combining, under gellation conditions in order to form agel, at least one aluminum source material, at least one phosphorussource material, at least one template, water, at least one co-solvent,and a silicon source material, the co-solvent being water-soluble andcapable of solubilizing the silicon source material, and then (b)reacting the gel under molecular sieve synthesis conditions.
 11. Themethod of claim 10 wherein the silicon source material is at least onealkoxide of silicon.
 12. The method of claim 11 wherein the aluminumsource material is at least one of hydrated alumina, organo alumina,pseudo-boehmite, aluminum hydroxide, and colloidal alumina.
 13. Themethod of claim 12 wherein the silicon source material is at least oneof tetramethylorthosilicate, tetraethylorthosilicate,tetrapropylorthosilicate, and tetrabutylorthosilicate.
 14. The method ofclaim 13 wherein the co-solvent is at least one of acetone,1,2-propanediol, 1,3-propanediol, methanol, ethanol, propanol,isopropanol, butanol, and ethylene glycol.
 15. The method of claim 14wherein the template is capable of structure directing to AEL and isselected from at least one of di-n-propylamine, diisopropylamine, anddiethylamine.
 16. The method of claim 15 wherein the phosphorus sourcematerial is one or more of H₃PO₄, and ammonium phosphate.
 17. The methodof claim 16 wherein the molecular sieve synthesis conditions includeheating the gel in an autoclave for a time sufficient to crystallize thegel at a temperature ranging from about 100° C. to about 250° C.
 18. Themethod of claim 17 further comprising combining the aluminum sourcematerial, the organic silicon source material, the phosphorus sourcematerial, water, the co-solvent, and the template with at least onesurfactant.
 19. The method of claim 18 wherein the surfactant is one ormore of hexadecylamine, tetradecylamine, dodecylamine, decylamine, oroctylamine, dimethylhexadecylammine or dimethyloctylamine, andtrimethylhexadecylammonium chloride.
 20. The method of claim 19 whereinthe template is di-n-propylamine.
 21. The method of claim 20 wherein thegel is heated in a microwave autoclave.
 22. The method of claim 21further comprising calcining the product of step (b).
 23. A molecularsieve product formed by (a) combining, under gellation conditions inorder to form a gel, at least one aluminum source material, at least onephosphorus source material, at least one template, water, at least oneco-solvent, and a silicon source material, the co-solvent being awater-soluble co-solvent and capable of solubilizing the silicon sourcematerial, and then (b) reacting the gel under molecular sieve synthesisconditions.
 24. The product-by-process of claim 23 wherein the siliconsource material is at least one alkoxide of silicon.
 25. Theproduct-by-process of claim 24 wherein the aluminum source material isat least one of hydrated alumina, organo alumina, pseudo-boehmite,aluminum hydroxide, and colloidal alumina.
 26. The product-by-process ofclaim 25 wherein the silicon source material is at least one oftetramethylorthosilicate, tetraethylorthosilicate,tetrapropylorthosilicate, and tetrabutylorthosilicate.
 27. Theproduct-by-process of claim 26 wherein the co-solvent is at least one ofacetone, 1,2-propanediol, 1,3-propanediol, methanol, ethanol, propanol,isopropanol, butanol, and ethylene glycol.
 28. The product-by-process ofclaim 27 wherein the template is at least one of di-n-propylamine,diisopropylamine, and diethylamine.
 29. The product-by-process of claim28 wherein the phosphorus source material is one or more of H₃PO₄, andammonium phosphate.
 30. The product-by-process of claim 29 wherein themolecular sieve synthesis conditions include heating the gel in anautoclave for a time sufficient to crystallize the gel at a temperatureranging from about 100° C. to about 250° C.
 31. The product-by-processof claim 30 further comprising combining the aluminum source material,the organic silicon source material, the phosphorus source material,water, the co-solvent, and the template with at least one surfactant.32. The product-by-process of claim 31 wherein the surfactant is one ormore of hexadecylamine, tetradecylamine, dodecylamine, decylamine, oroctylamine, dimethylhexadecylammine or dimethyloctylamine, andtrimethylhexadecylammonium chloride.
 33. The product-by-process of claim32 wherein the template is di-n-propylamine.
 34. The product-by-processof claim 33 wherein the gel is heated in a microwave autoclave.
 35. Theproduct-by-process of claim 34 further comprising calcining themolecular sieve product of step (b) in order to form a calcinedmolecular sieve product.
 36. A silicoaluminophosphate gel formed bycombining under gellation conditions at least one aluminum sourcematerial, at least one phosphorus source material, at least onetemplate, water, at least one co-solvent, and a silicon source material,the co-solvent being water-soluble and capable of solubilizing thesilicon source material.
 37. The gel of claim 36 wherein the gel has theformula X₁SURF:X₂TEMP:Al₂O₃:P₂O₅:X₃SiO₂:X₄H₂O:X₅SOL and X₁ ranges fromabout 0 to about 0.5, X₂ ranges from about 0.1 to about 4, X₃ rangesfrom about 0.01 to about 2, X₄ ranges from about 10 to about 100, and X₅ranges from about 4 to about
 20. 38. A composition comprising amolecular sieve with a framework tetrahedra of silicon, aluminum, andphosphorus, the composition having a total silicon amount ranging fromabove about 5 molar percent to about 15 molar percent, a total aluminumamount ranging from about 40 molar percent to about 55 molar percent,and a total phosphorus amount ranging from about 30 molar percent toabout 50 molar percent, the molar percents being based on the totalamount of aluminum, phosphorus, and silicon present in the composition,and the molecular sieve having the topology AEL, wherein (a) more thanabout 90 molar % of the silicon atoms in the framework have at least onealuminum atom nearest neighbor, (b) the number of Si atoms in theframework having three Si nearest neighbors ranges from about 0 mol. %to about 25 mol. %, the mol. % being based on the total amount ofsilicon in the framework and measured by ²⁹Si MAS NMR, (c) the molecularsieve has a crystal size ranging from about 0.001 micrometers to about1.0 micrometers, and (d) the molecular sieve is in the form of plateletshaving a first thickness in the direction and a second thickness in thedirection, the second thickness being greater than the first thickness,and the first thickness being less than 50 nm.
 39. A compositioncomprising a molecular sieve with a framework tetrahedra of silicon,aluminum, and phosphorus, the composition having a total silicon amountranging from above about 4 molar percent to about 20 molar percent, atotal aluminum amount ranging from about 40 molar percent to about 55molar percent, and a total phosphorus amount ranging from about 30 molarpercent to about 50 molar percent, the molar percents being based on thetotal amount of aluminum, phosphorus, and silicon present in thecomposition, and the molecular sieve having the topology AEL, wherein(a) more than about 50 molar % of the silicon atoms in the frameworkhave at least one aluminum atom nearest neighbor and (b) the number ofSi atoms in the framework having three Si nearest neighbors ranges fromabout 0 mol. % to about 25 mol. %, the mol. % being based on the totalamount of silicon in the framework and measured by ²⁹Si MAS NMR.
 40. Themethod of claim 39 wherein the molecular sieve has a crystal sizeranging from about 0.001 micrometers to about 1.0 micrometers.
 41. Themethod of claim 40 wherein the molecular sieve is in the form ofplatelets having a first thickness in the direction and a secondthickness in the direction, the second thickness being greater than thefirst thickness, and the first thickness being less than 50 nm.